The traditional implantable cardiac pacemaker includes a pulse generator device to which one or more flexible elongate lead wires are coupled. The device is typically implanted in a subcutaneous pocket, remote from the heart, and each of the one or more lead wires extends therefrom to a corresponding electrode, coupled thereto and positioned at a pacing site, either endocardial or epicardial. Mechanical and/or MRI compatibility issues, which are sometimes associated with elongate lead wires and well known to those skilled in the art, have motivated the development of implantable cardiac pacing devices that are wholly contained within a relatively compact package, the entirety of which is configured for implant in close proximity to the pacing site. Such a medical device and a corresponding catheter assembly that is configured as a delivery tool for the device are described in the commonly assigned United States Patent Application US 2015/0094668. A schematic diagram in FIG. 1 shows potential cardiac implant sites to which the described delivery tool may deliver the device, for example, within an appendage 102 of a right atrium RA, or in proximity to an apex 103 of a right ventricle RV.
With further reference to FIG. 1, alternative implant sites for the device are on the left side of the heart, for example, within a coronary vein CV, which may be accessed through a coronary sinus ostium CSOS, or within the left ventricle (not seen), which may be accessed through an orifice created through (into the page) an interatrial septum IS in the area of appendage 102. But an operator may encounter some difficulty in navigating a catheter assembly/delivery tool like that described in the '668 reference to these sites on the left side of the heart.